text: """
  xgal.model
  
  Contains functions and classes for converting parameters
  to a prediction for the gk and gg data vectors.
  
  """
  
  def cl(spec,params,zs=None,dndz=None,backend="camb"):
      assert backend in ['orphics','hmvec','camb','ccl']
      assert spec in ['kk','kg','gg']
  
      if backend=='orphics':
          from orphics import cosmology
          lc = cosmology.LimberCosmology(params,skipCls=True)
          
          
      elif backend=='hmvec':
          pass
      elif backend=='camb':
          pass
      elif backend=='ccl':
          pass
  